A significant consideration when designing many electronic circuits is the need to provide a low impedance power supply and ground node. In effect, as the current drawn by devices within the circuit varies with time, the actual supply and ground voltages seen by the circuit are determined by the current drawn from the supply and ground nodes and their respective impedances. As such, if the impedances are maintained low enough, the power supply and ground nodes may approach their ideal DC values even with the variation of supply and ground current, and the circuit may operate as desired.
With the advent of dense integrated circuits and the packages and circuit boards that support them, numerous undesired impedances appear in the supply and ground nodes. In addition, higher switching speeds of CMOS circuits result in significantly greater supply and ground transient currents than prior technologies. Hence, to establish the desired impedance at a supply or ground node, capacitors are typically placed at strategic points on an integrated circuit and/or within the integrated circuit package and/or on the circuit board such that the high frequency impedance of the supply and ground nodes is reduced to an acceptable level. These capacitors are often referred to as decoupling or bypass capacitors.
While known decoupling capacitors may reduce power supply voltage transients, new decoupling strategies are needed to meet the needs of current and future highly demanding integrated circuit designs.